A world-leading seismic retrofit

Beca's retrofit of 8 Willis Street turned a building that no longer met the market’s requirements for seismic performance into one of Wellington’s most resilient workspaces.

Our breakthrough in structural analysis enabled us to add five floors to the 1980s tower at 8 Willis Street. It already had eight storeys, but we extended the footprint and brought the structure up to market-leading seismic resilience – achieved with just 12 large fluid viscous dampers and a minimally invasive structural retrofit.

This cutting-edge approach involved modelling the location of dampers, shear walls and other structural components, and testing the design against dozens of historic earthquake records from around the world. 

The building’s commercial prospects were transformed. The retrofitted 1980s tower links to a new development at Stewart Dawson’s Corner, which cantilevers over the historic 1900s building – our work included strengthening the landmark façade and renovating original timber roof.

Our seismic upgrade has delivered the benefits of a new build, but in less time and at lower cost. Minimal work was required on the building’s foundations, further simplifying the construction programme, and thousands of tonnes of concrete were retained in situ– a big sustainability dividend.
 
The result is a 12,300m² modern, open plan workspace rated at 130%NBS (IL2). The retrofitted 1980s building has a clean interior, free from the intrusive structural interventions that would normally be required to achieve such a high level of resilience. In fact, there are more floors without dampers than with them.

Our game-changing structural optimisation work is equally applicable for retrofit and new build projects – opening the door to buildings that are more resilient, less complex to construct and with a reduced carbon footprint.

Awards

• John Hollings 'Seismic Resilience in Practice' Award
• Award of Excellence (Structural) – Council for Tall Buildings and Urban Habitat 2023 Awards
• 2022 IStructE Structural Awards – Winner

"A well-considered project highlighting the value that the structural engineer brought to the project. Fluid viscous dampers have been used in a technical and elegant way to significantly improve earthquake resistance of the building. The thoughtful placement of the dampers has maintained open spaces, uninhibited by the structure, unlike other highly resilient seismic retrofits and new builds, where primary structural components tend to dominate the interior." - Judges comments from the IStructE Structural Awards.